continuous grounding conductor
- Thread starter rsimp1967
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Re: continuous grounding conductor
Dereck: Instead of connecting the service ground electrode conductors and transformer ground conductors, separately to the water pipe, connect the transformer ground conductor to the service neutral/ground buss.
Now everything is grounded with no common mode voltage or current.
Dereck: Instead of connecting the service ground electrode conductors and transformer ground conductors, separately to the water pipe, connect the transformer ground conductor to the service neutral/ground buss.
Now everything is grounded with no common mode voltage or current.
Re: continuous grounding conductor
Bennie, I am glad you got to the N-G bond point. I understand the CM problems you are talking about from taking ground references at different points on closed ground loops. It is a reality in any electrical distribution system.
But there is a way to deal with it when serving sensitive equipment, which is an isolation transformer or any transformer for that matter. A transformer forms a new N-G bond point from which a new single point ground can be established. It doesn't matter what is going on before the N-G bond. Indeed there will be some voltage at that point from CM. But all down stream equipment from the new N-G bond point sees it at the same potential and thereby no effect downstream unless you add another loop to inject CM current?.
Bennie, I am glad you got to the N-G bond point. I understand the CM problems you are talking about from taking ground references at different points on closed ground loops. It is a reality in any electrical distribution system.
But there is a way to deal with it when serving sensitive equipment, which is an isolation transformer or any transformer for that matter. A transformer forms a new N-G bond point from which a new single point ground can be established. It doesn't matter what is going on before the N-G bond. Indeed there will be some voltage at that point from CM. But all down stream equipment from the new N-G bond point sees it at the same potential and thereby no effect downstream unless you add another loop to inject CM current?.
- Location
- Illinois
- Occupation
- retired electrician
Re: continuous grounding conductor
Bennie,
In my opinion, the connections on the building steel that hold the building together are of low enough resistace for the purpose of a grounding electrode. In the case of the transformer in the wooden building, there would be no problem in driving two ground rods to serve as the grounding electrode for the transformer. This new grounding electode will be bonded to the service grounding electrode by the transformer feeder equipment grounding conductor. You could also use the exception to 250.30(A)(4) to run the grounding electrode conductor back to the service grounding electrode system.
Don
Bennie,
In my opinion, the connections on the building steel that hold the building together are of low enough resistace for the purpose of a grounding electrode. In the case of the transformer in the wooden building, there would be no problem in driving two ground rods to serve as the grounding electrode for the transformer. This new grounding electode will be bonded to the service grounding electrode by the transformer feeder equipment grounding conductor. You could also use the exception to 250.30(A)(4) to run the grounding electrode conductor back to the service grounding electrode system.
Don
Re: continuous grounding conductor
A ground electrode conductor is an inductor.
A bonding conductor is a short circuit.
Feeding two ground electrodes from one point is not bonding, it is parallel feeding two ground points. There will be two ground electrode systems at a different potential.
A ground electrode conductor is an inductor.
A bonding conductor is a short circuit.
Feeding two ground electrodes from one point is not bonding, it is parallel feeding two ground points. There will be two ground electrode systems at a different potential.
Re: continuous grounding conductor
I think bennie left-out at least one or more stipulation.
"A ground(ing) electrode conductor is an INDUCTOR"
"A Bonding conductor is a SHORT CIRCUIT"
a third or fourth assumption, or more, from the above would be;
An inductor is a short circuit, or
A short circuit is an inductor.
I have drove ground rods in the earth 10' apart and on a cheap VOM, a voltage of just over 1.0 volts DC was measured between the rods. This was over 40 years ago.
There will always be current between electroded spaces apart.
For Grounding puposes, there should not be objectional current on these conductors UNLESS there is a fault of the Circuit Conductors insulation, that is from the voltage source to the load and then back to the voltage source.
If there is a fault condition, then the current through the Grounding conductor(s) would be objectional to the normal circuit ( during the fault), but the grounding is required to open any OCPD protecting the ungrounded conductor.
Glenn
I think bennie left-out at least one or more stipulation.
"A ground(ing) electrode conductor is an INDUCTOR"
"A Bonding conductor is a SHORT CIRCUIT"
a third or fourth assumption, or more, from the above would be;
An inductor is a short circuit, or
A short circuit is an inductor.
I have drove ground rods in the earth 10' apart and on a cheap VOM, a voltage of just over 1.0 volts DC was measured between the rods. This was over 40 years ago.
There will always be current between electroded spaces apart.
For Grounding puposes, there should not be objectional current on these conductors UNLESS there is a fault of the Circuit Conductors insulation, that is from the voltage source to the load and then back to the voltage source.
If there is a fault condition, then the current through the Grounding conductor(s) would be objectional to the normal circuit ( during the fault), but the grounding is required to open any OCPD protecting the ungrounded conductor.
Glenn
Re: continuous grounding conductor
Glenn: Two rods ten feet apart will read a voltage due to being an open or high impedance circuit. Bonding (shorting) the two will eliminate the voltage difference.
Current flow in an inductor will oppose itself, creating a difference in potential between the two ends.
Glenn: Two rods ten feet apart will read a voltage due to being an open or high impedance circuit. Bonding (shorting) the two will eliminate the voltage difference.
Current flow in an inductor will oppose itself, creating a difference in potential between the two ends.
- Location
- Illinois
- Occupation
- retired electrician
Re: continuous grounding conductor
Bennie,
How are these two installations electrically different?
1) Two grounding electrodes are connected via two grounding electrode conductors to the main bonding jumper at the service disconnect.
2) The first grounding electrode is connected to the main bonding jumper at the service equipment via a grounding electrode conductor and the second grounding electrode is connected to the first grounding electrode via an extension of the first grounding electrode conductor.
Don
Bennie,
How are these two installations electrically different?
1) Two grounding electrodes are connected via two grounding electrode conductors to the main bonding jumper at the service disconnect.
2) The first grounding electrode is connected to the main bonding jumper at the service equipment via a grounding electrode conductor and the second grounding electrode is connected to the first grounding electrode via an extension of the first grounding electrode conductor.
Don
Re: continuous grounding conductor
Parallel conductors create common mode voltage.
Series conductor carries common mode current.
Common mode voltage causes circulating common mode current.
Common mode current causes noise, voltage gradients, false signals, and general garbage.
Parallel conductors create common mode voltage.
Series conductor carries common mode current.
Common mode voltage causes circulating common mode current.
Common mode current causes noise, voltage gradients, false signals, and general garbage.
Re: continuous grounding conductor
I neglected to note in the previous post that the ground rod(s) , as per the plans, were to be of a delta connected grounding array at a second building.
So they were to be the Ground Electrode.
At that time, I was installing per the prints. Really didn't pay much attention to the NEC when on industrial premise. I was much younger and didn't argue very often with the superiors. If installed per the NEC, it would most likely have been the 1959 or maybe the 1956 issue.
This particular plant used Poco power as well as plant generated power. If I remember correctly, the Plant Engineer said they could generate power at 7 mils ($0.007) per kilowatt.
Glenn
I neglected to note in the previous post that the ground rod(s) , as per the plans, were to be of a delta connected grounding array at a second building.
So they were to be the Ground Electrode.
At that time, I was installing per the prints. Really didn't pay much attention to the NEC when on industrial premise. I was much younger and didn't argue very often with the superiors. If installed per the NEC, it would most likely have been the 1959 or maybe the 1956 issue.
This particular plant used Poco power as well as plant generated power. If I remember correctly, the Plant Engineer said they could generate power at 7 mils ($0.007) per kilowatt.
Glenn
Ed MacLaren
Senior Member
Re: continuous grounding conductor
The sketches below represent a few of the many ways that a "system" could be grounded. Assume that any junctions shown in Grounding Electrode Conductors are made by acceptable methods.
In my opinion, both A and B are "single point grounding" and would be code compliant, while both C and D represent "multi-point grounding" and would be code violations.
I'd like some opinions on this.
Ed
The sketches below represent a few of the many ways that a "system" could be grounded. Assume that any junctions shown in Grounding Electrode Conductors are made by acceptable methods.
In my opinion, both A and B are "single point grounding" and would be code compliant, while both C and D represent "multi-point grounding" and would be code violations.
I'd like some opinions on this.
Ed
Re: continuous grounding conductor
Ed: Super drawings. On D remove the green wire from the panel buss to the ground rod and this will be single point grounding on a multi-ground neutral system.
Drawing B is single point grounding on a multi-ground neutral system.
The others are all multi point due to different potential at each point. You can not call two nodes one.
Ed: Super drawings. On D remove the green wire from the panel buss to the ground rod and this will be single point grounding on a multi-ground neutral system.
Drawing B is single point grounding on a multi-ground neutral system.
The others are all multi point due to different potential at each point. You can not call two nodes one.
Re: continuous grounding conductor
As usual, Ed has some great diagrams.
Making a DC voltage and current calculation ( because I am not confident of doing AC voltage and current calculations), is the following a reasonable approach?
Table 8 of Chapter 9 shows 4AWG copper to have .308 ohms resistance at 1000 feet.
All of Ed's Ground Electrodes ( GE ) of diagram "A" and "B" would require a minimum of a 4 AWG copper between them except for the Ground Rods ( NEC Table 250.56 ).
Assumptions for this calculation;
All Bonding conductors between the GE's are 4 AWG.
Earth, as a generator, produces a maximum of 2 DC volts between any GE's.
Minimum ohms between any two GE's is 25 ohms ( 250.56 ).
All GE's are at least 10' apart.
The earth, as a generator, cannot maintain more than .002 DC volts between the GE's when bonded by a 4 AWG copper Bonding Jumper (BJ). [ just a SWAG value].
10' of 4 AWG is .308 ohms / 1000' x 10' = .00308 ohms.
I = E / R
I = .002Vdc / .00308 ohms = .64935 DC Amps.
Greater distances between the GE's would reduce th the DC current flow. Now this is just the earth acting as a battery ( generator ).
The main point about Ed's "A" and "B" diagrams with the multiple GE's is that the voltage potential and any current flow should only be during times of a circuit fault of the ungrounded conductor trying to bypass the grounded conductor path back to the voltage source if the circuit, which should not be often and preferably never.
If there is a Ground current problem with sensitive electronic equipment, let the equipment manufacture filter it out when the power grounding meets the NEC requirements.
Personnaly, I doubt if very many old installations actually meet all the grounding requirements of NEC 250.
Correct them first.
Glenn
As usual, Ed has some great diagrams.
Making a DC voltage and current calculation ( because I am not confident of doing AC voltage and current calculations), is the following a reasonable approach?
Table 8 of Chapter 9 shows 4AWG copper to have .308 ohms resistance at 1000 feet.
All of Ed's Ground Electrodes ( GE ) of diagram "A" and "B" would require a minimum of a 4 AWG copper between them except for the Ground Rods ( NEC Table 250.56 ).
Assumptions for this calculation;
All Bonding conductors between the GE's are 4 AWG.
Earth, as a generator, produces a maximum of 2 DC volts between any GE's.
Minimum ohms between any two GE's is 25 ohms ( 250.56 ).
All GE's are at least 10' apart.
The earth, as a generator, cannot maintain more than .002 DC volts between the GE's when bonded by a 4 AWG copper Bonding Jumper (BJ). [ just a SWAG value].
10' of 4 AWG is .308 ohms / 1000' x 10' = .00308 ohms.
I = E / R
I = .002Vdc / .00308 ohms = .64935 DC Amps.
Greater distances between the GE's would reduce th the DC current flow. Now this is just the earth acting as a battery ( generator ).
The main point about Ed's "A" and "B" diagrams with the multiple GE's is that the voltage potential and any current flow should only be during times of a circuit fault of the ungrounded conductor trying to bypass the grounded conductor path back to the voltage source if the circuit, which should not be often and preferably never.
If there is a Ground current problem with sensitive electronic equipment, let the equipment manufacture filter it out when the power grounding meets the NEC requirements.
Personnaly, I doubt if very many old installations actually meet all the grounding requirements of NEC 250.
Correct them first.
Glenn
Re: continuous grounding conductor
Current flows on the ground electrode conductor at all times, even with the main switch open.
Equipment designed to operate and filter garbage signals will be too expensive to purchase.
Cheaper to route ground conductors to reduce or eliminate common mode current flow.
Current flows on the ground electrode conductor at all times, even with the main switch open.
Equipment designed to operate and filter garbage signals will be too expensive to purchase.
Cheaper to route ground conductors to reduce or eliminate common mode current flow.
Re: continuous grounding conductor
Ed, ?A? is single point grounding. There would be some minute common mode current flow between the ground electrodes. But it would not cause any problems down stream from the N-G bond point, since the voltage developed would be at the same potential or reference. The key installation issue is to keep all the GEC?s grouped together side-by-side, and making the MBJ and EGC adjacent to one another.
?B? is another single point ground. This closely resembles the method used by all telephone companies, and is the recommended practice by ANSI, BICSI, Bellcore TIA/EIA, and others. Again small amounts of common mode current will flow between ground electrodes, but again as in ?A? the SPG eliminates any problems.
C&D are both code violations. ?D? is a multi-grounded-neutral, and significant current would flow in the GEC. ?C? looks a lot like a service entrance, but would not be allowed on premises wiring.
Again I would like to point out that true single point grounding is extremely rare, and not possible in most circumstances. To have truly SPG would require complete electrical isolation of all raceways and equipment downstream from the N-G bond point. There could be no incidental or intentional contact with any type of ground like cement, rebar, building steel, or any conductive surface. Very few industries even attempt to pull it off. Its reward is great if you can do it. It would be impossible for lightning current and common mode current to flow.
Ed, ?A? is single point grounding. There would be some minute common mode current flow between the ground electrodes. But it would not cause any problems down stream from the N-G bond point, since the voltage developed would be at the same potential or reference. The key installation issue is to keep all the GEC?s grouped together side-by-side, and making the MBJ and EGC adjacent to one another.
?B? is another single point ground. This closely resembles the method used by all telephone companies, and is the recommended practice by ANSI, BICSI, Bellcore TIA/EIA, and others. Again small amounts of common mode current will flow between ground electrodes, but again as in ?A? the SPG eliminates any problems.
C&D are both code violations. ?D? is a multi-grounded-neutral, and significant current would flow in the GEC. ?C? looks a lot like a service entrance, but would not be allowed on premises wiring.
Again I would like to point out that true single point grounding is extremely rare, and not possible in most circumstances. To have truly SPG would require complete electrical isolation of all raceways and equipment downstream from the N-G bond point. There could be no incidental or intentional contact with any type of ground like cement, rebar, building steel, or any conductive surface. Very few industries even attempt to pull it off. Its reward is great if you can do it. It would be impossible for lightning current and common mode current to flow.
- Location
- Illinois
- Occupation
- retired electrician
Re: continuous grounding conductor
Bennie,
How are they not shorted in A?
don
Bennie,
How are they not shorted in A?
don
Re: continuous grounding conductor
Bennie they are shorted. They are terminated on a bus bar in close proximity to each other. It doesn't get any better than that. It is a ground plane, not a wire bus.
In my designs I install a copper bus bar (called a principle ground point) near but adjacent to the AC switchgear and terminate the GE's radially as shown in diagram "A", then run a single conductor to the neutral bus of the switch gear.
Bennie they are shorted. They are terminated on a bus bar in close proximity to each other. It doesn't get any better than that. It is a ground plane, not a wire bus.
In my designs I install a copper bus bar (called a principle ground point) near but adjacent to the AC switchgear and terminate the GE's radially as shown in diagram "A", then run a single conductor to the neutral bus of the switch gear.
Re: continuous grounding conductor
A nodal analysis of each electrode at the electrode connection, will show a different voltage. This is not an equi-potential plane.
Bonding, (shorting) to electrically become one electrode, will not produce different voltage at each connection point. The area will be an equi-potential plane.
Separate the various electrodes 50 feet, and tell me this is single point grounding.
My definition of single point ground is single point ground (as in earth) not as in buss bars.
[ April 14, 2003, 12:43 AM: Message edited by: bennie ]
A nodal analysis of each electrode at the electrode connection, will show a different voltage. This is not an equi-potential plane.
Bonding, (shorting) to electrically become one electrode, will not produce different voltage at each connection point. The area will be an equi-potential plane.
Separate the various electrodes 50 feet, and tell me this is single point grounding.
My definition of single point ground is single point ground (as in earth) not as in buss bars.
[ April 14, 2003, 12:43 AM: Message edited by: bennie ]
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